Adding a modbus sensor is pretty easy. Follow developer guide in this section, copy eg sdm120.json to be your template (https://raw.githubusercontent.com/boneIO-eu/app_black/dev/boneio/sensor/modbus/sdm120.json)
Make your new file, test it, put it in boneio/sensor/modbus/{model}.json
directory. Make PR to application with this file.
New config will be available then for all boneIO users!